The new owner of one of the biggest office projects on the Dallas North Tollway is about to begin renovations.

New York-based Fortis Property Group bought the three-building Colonnade high-rise project in April.

The more than 1 million-square-foot office complex in Addison was built in the late 1980s and 1990s.

Fortis Property CEO Jonathan Landau said Wednesday that his firm plans to start remodeling next month.

“We are going to make some great improvements to the buildings,” Landau said.

Most of the redo will concentrate on the atrium that connects the three office towers. But Fortis also plans to make changes in the lobby areas of the buildings and upgrade the elevators.

“We have a great new design for the atrium that will create a more pleasant atmosphere for our tenants,” Landau said. “The challenge when you take a 1980s building and try to modernize it is to make it look cohesive.

“We are going to try and make it a very uniform feel.”

Dallas design firm Staffelbach is in charge of the makeover.

The work should be done by the end of the year.

Cushman & Wakefield handles leasing for the buildings, which are more than 90 percent leased.

“We’ve done a bunch of new leasing and tenant renewals,” Landau said.

Fortis’ purchase of the Colonnade from CBRE Global Investors is one of the largest office investments in the Dallas area so far in 2013. The project sold for nearly $200 million.

Fortis bought the office buildings after selling some tollway properties — including the Galleria office towers — before the recession.

“We were lucky enough to sell right before the crash,” Landau said. “And we were looking for the opportune time to get back in that market.”

Fortis also owns the Harwood Center tower in downtown Dallas and the NEC office complex in Las Colinas.

“Right now we are crossing our fingers that the fundamentals in Dallas continue to be strong,” Landau said. “We think there are still opportunities to buy properties on the Dallas North Tollway and certainly in Las Colinas.”